1. Field of the Invention
The present invention relates to a radio communications system and method for a multimedia broadcast and multicast (MBMS) service, and particularly, to a signaling transmission method for receiving an MBMS service notification.
2. Description of the Background Art
A universal mobile telecommunications system (UMTS) is a third generation mobile communications system that has evolved from a specification known as the European Global System for Mobile communications (GSM) system which aims to provide an improved mobile communications service based on a GSM core network and a wideband code division multiple access (W-CDMA) technology.
FIG. 1 illustrates a network structure of a UMTS system to which the conventional art and the present invention are applied.
As illustrated in the drawing, the UMTS system is broadly comprised of a terminal (or user equipment: UE), a UTRAN and a Core Network (CN). The UTRAN includes more than one Radio Network Sub-system (RNS), each of which includes a single Radio Network Controller (RNC) and more than one Node B managed by the RNC. The RNC manages the Node B which serves as an access point of the UTRAN for the terminal by receiving information transmitted from a physical layer of the terminal over an uplink and transmitting data to the terminal over a downlink. The RNC allocates and manages radio resources, and serves as an access point of the CN.
FIG. 2 illustrates a connection structure between the UTRAN and the terminal within the UMTS network.
Referring to FIG. 2, the terminal is connected with the CN to thusly receive services provided from the UMTS, and information of the terminal and the CN is transmitted via the UTRAN. The CN is connected to the RNC through an lu interface so as to transmit and receive data and control messages. Each terminal connected to the UMTS network is managed by a specific RNC within the UTRAN. A Serving RNC (SRNC) is the RNC for managing terminals. In other words, the SRNC refers to the RNC which serves as the access point with the CN for transmitting data to a specific terminal. The SRNC performs as a second layer of an Open System Interface (OSI) for data coming through a radio interface or being transmitted to the terminal, and allocates radio resources appropriate to provide services. The function of managing radio resources performed by the SRNC includes control functions associated with the specific terminal such as functions of setting transport channels, determining a handover, performing an Open Loop Power Control, and so on. The terminal connected to the CN through the UTRAN at a specific time point has only one SRNC.
In general, one RNC is used between the terminal and the CN. However, if the terminal moves to an area managed by another RNC, the terminal is connected to the SRNC via the RNC of the corresponding area.
The terminal is initially connected to the CN through an R1 (RRC1). However, if the terminal moves to an area (cell) managed by an R2 (RAN2), the terminal is connected to the R1 through an lur interface via the R2. In this case, the R1 manages the terminal and serves as an access point with the CN, and the R2 partially performs functions of simply routing user data or allocating common resources. In the UMTS network, every RNC such as the R2 connected to the terminal other than the SRNC is referred to as a Drift RNC (DRNC). Thus, one terminal may have no DRNC or may have one or several DRNCs according to the connection state thereof.
The SRNC and the DRNC are logically divided with relation to a specific terminal. However, the RNC and the Node B within the UTRAN have a subordinate relation therebetween, and accordingly the RNC can be divided at the side of the Node B. That is, in order to distinguish between the RNC for managing the Node B itself and other RNCs, an RNC for managing a specific Node B is referred to as a Controlling RNC (CRNC). Namely, the RNC which is connected to the Node B via an lub and controls radio resources of the Node B, corresponds to the CRNC of the corresponding Node B, and has a one-to-many relation between the CRNC and the Node B in the structure of the UTRAN. The CRNC performs functions such as load control and congestion control of traffic within a cell that the CRNC itself manages, acceptance control for a new radio link set within this cell and a code allocation.
A Radio Resource Control (RRC) layer is defined at a third layer of a radio protocol located in the RNC and the terminal. The RRC handles the controlling of transport channels and physical channels related to establishment, reconfiguration, and release of Radio Bearers (RBs). In this case, the RB denotes the services provided by a second layer of the radio protocol for data transmissions between the terminal and the RNC. In general, establishing the RB denotes the processes of stipulating the characteristics of a protocol layer and a channel, which are required for providing a specific service, and setting the respective detailed parameters and operation methods thereof.
An RRC state of the terminal and an RRC connection method will now be explained.
The RRC state refers to whether the RRC of the terminal is logically connected to (forms a logical connection with) the RRC of the UTRAN. If the RRC of the terminal forms the logical connection with the RRC of the UTRAN, this is referred to as an RRC connected state. Conversely, if there is no logical connection therebetween, this is referred to as an RRC idle state. If the terminal is in the RRC connected state, and accordingly the UTRAN can recognize the existence of the corresponding terminal according to units of cells, thereby effectively controlling the terminal. On the other hand, the UTRAN can not recognize a terminal that is in idle state. The terminal in idle state can be managed by the CN according to units of location areas or units of routing areas which are areas greater than the cell. That is, the existence of a terminal in idle state is only recognized according to units of large areas (location areas or routing areas), and the terminal must change into the connected state in order to receive typical mobile communication services such as voice or data.
FIG. 3 is a diagram illustrating an RRC state transition of the terminal.
As illustrated in FIG. 3, when a user turns on the power of the terminal, the terminal first detects an appropriate cell and maintains its idle state in the corresponding cell. The terminal in idle state forms an RRC connection with the RRC of the UTRAN through the RRC connection procedure and is then transited into the RRC connected state when the RRC connection needs to be formed. There are several cases that the terminal in idle state is required to form the RRC connection. For instance, there may be such cases that an uplink data transmission is required due to a call attempt by a user, or when the transmission of a response message in response to a paging message received from the UTRAN is required.
Hereinafter, a Multimedia Broadcast/Multicast Service (MBMS) will now be described.
The MBMS refers to a service for providing streaming or background services to a plurality of terminals using a downlink dedicated MBMS bearer service. In the UTRAN, the MBMS bearer uses a point-to-multipoint radio bearer (RB) and a point-to-point RB.
The MBMS is divided into a broadcast mode and a multicast mode. The MBMS broadcast mode is a service for transmitting multimedia data to all users within a broadcast area. Here, the broadcast area refers to a region where the broadcast service is possible. Conversely, the MBMS multicast mode is a service for transmitting the multimedia data only to a specific user group within a multicast area. Here, the multicast area refers to a region where the multicast service is possible. The multimedia area and broadcast area are referred to as a service area.
FIG. 4 shows a procedure for providing a specific MBMS service (service 1) from a UMTS network to a terminal (UE) by using a multicast mode.
A UE1 that wants to receive an MBMS service subscribes to the service 1 (Subscription). Here, subscribing refers to establishing a relationship between a service provider and a user. Terminals to desirably receive the MBMS service should receive a service announcement provided by the network. Here, the service announcement refers to providing to the terminal an index and any related information of the services to be provided. In particular, a terminal to desirably receive the MBMS service of the multicast mode should join a multicast group. Here, the multicast group refers to a group of terminals receiving a specific multicast service, and joining refers to one user merging with the other users in a multicast group who congregates to receive the particular multicast service. The terminal can inform the UMTS network that it desires to receive specific multicast data through MBMS multicast joining. On the contrary, a procedure that a terminal having joined a specific multicast group releases its joining with respect to the multicast group is referred to as leaving. Each terminal performs such subscribing, joining and leaving processes. The terminal can perform the subscribing, joining, and leaving processes at various times, such as before data transmission, during the transmission, or after the transmission.
While a specific MBMS service is ongoing, one or more sessions can sequentially be generated with respect to the corresponding service. If data to be transmitted for the specific MBMS service is generated in an MBMS service source, the CN notifies a session starting to the RNC. On the contrary, when there is no more data to be transmitted for the specific MBMS service in the MBMS service source, the CN notifies a session stop to the RNC. The data transmission with respect to the specific MBMS service can be carried out between the session starting and the session stop. At this time, the data transmitted through the data transmission process can be transmitted only to the terminals having joined the multicast group for the specific MBMS service.
In the session starting process, the RNC having received the session starting from the CN transfers an MBMS notification to the terminals. Here, the MBMS notification refers to the RNC informing a terminal that the data transmission of the specific MBMS service in a cell draws near (is impending). The MBMS notification is transmitted more than one time before actual data of the service is transmitted. When carrying out the MBMS notification process, the UTRAN may also count the number of terminals receiving the specific MBMS service within one specific cell. The counting procedure is used for determining whether a point-to-multipoint RB or a point-to-point RB should be set as the RB for transmitting the specific MBMS service, or whether no RB should be set.
The RNC internally establishes a threshold value to select an appropriate MBMS RB. After the RNC counts the number of terminals, if the counted number of terminals existing within the corresponding cell is smaller than the threshold value, the RNC establishes the point-to-point RB, while the point-to-multipoint RB is established, if the counted number of terminals is greater than the threshold value. Thus, after determining the MBMS RB, the RNC informs the terminals of the establishment information of the corresponding RB. When the point-to-point RB is established for the specific service, the terminals desirably receiving the service are all in the RRC connected mode state. However, when the point-to-multipoint RB is established for the specific service, all terminals desirably receiving the service do not have to be in the RRC connected mode state. That is, terminals in an idle state can also receive the MBMS service data by using the point-to-multipoint RB. However, if there is no terminal counted which desires to receive the specific MBMS service, the RNC does not establish any RB and does not transmit the MBMS service data. That is why the establishing of an RB by the RNC, even if there is no user who wants to receive the service, causes undesirable consumption of radio resources. When MBMS service data is transmitted from the CN during one session of the MBMS service, the RNC initiates data transmission using the established RB, and releases the pre-established RB when the CN transmits a session stopping message.
The MBMS service area refers to an area configured with cells supporting MBMS services to which a specific terminal has subscribed. The MBMS service area is constructed by combining more than one cell, and may be constructed with cells managed by one RNC or be located over areas managed by several RNCs. A list of neighboring cell information refers to a list including information of cells managed by the DRNC which is positioned adjacent to the RNC.
FIG. 5 illustrates an MBMS attaching procedure.
Referring to the drawing, the RNC providing MBMS services recognizes and manages a terminal in the RRC connected mode state among terminals having joined a specific MBMS service for every cell that the RNC itself manages. For this, the RNC makes a list of terminals in the RRC connected mode (RRC connected mode terminal list) for each MBMS service of each cell. The RRC connected mode terminal list includes identifiers (URNTI) of the terminals having joined the specific MBMS service.
In such MBMS attaching procedure, among the MBMS services that the terminal in the RRC connected mode state has joined, for ongoing MBMS services, when the terminal has moved from a cell managed by the SRNC into a cell managed by the DRNC, and for MBMS services which are not ongoing, when the terminal has moved from the cell managed by the SRNC to the cell managed by the DRNC and thereafter the SRNC receives a session starting message from the CN with respect to the corresponding MBMS services, the SRNC transmits terminal information to the DRNC through an MBMS connection (attachment) request message, such that the DRNC adds terminals (which request the MBMS connection) to the RRC connected mode terminal list which the DRNC itself manages with respect to the MBMS services. At this time, the MBMS connection request message includes an ID of a cell to which the terminal has moved, IDs of MBMS services that the terminal is joining, the URNTI of the terminal, and the like.
Once receiving the MBMS connection (attachment) request message for a specific terminal from the SRNC, if it is possible to allocate resources for maintaining the RRC connected mode state with respect to the corresponding terminal, the DRNC grants the MBMS connection request of the terminal. The DRNC then adds the URNTI of the corresponding terminal to the RRC connected mode terminal list for the MBMS services in which the terminal having moved has joined.
Afterwards, the DRNC transmits a positive response to the SRNC through an MBMS connection response message. The SRNC having received the message continuously maintains the terminal in the RRC connected mode state even in the moved cell. The SRNC also transmits the MBMS service data to the terminal using a point-to-point RB. That is, the MBMS service data is transmitted to the DRNC through the SRNC and then transmitted to the terminal through the DRNC using the point-to-point RB.
The DRNC does not always grant the MBMS connection request when receiving the MBMS connection request message for the specific terminal from the SRNC. If the DRNC forms the RRC connection for the terminal but there are no resources for maintaining the terminal in the RRC connected mode state, the DRNC denies the MBMS connection request of the terminal and transmits a negative response to the SRNC.
However, in the conventional art, if the terminal located outside each MBMS service area is connected to the DRNC, there may occur the following problems.
In general, when the terminal positioned in another service area or outside the MBMS service area is connected to the DRNC positioned in a service area in which a service subscribed by the terminal can be supported, the corresponding terminal receives an MBMS notification of the DRNC to which the terminal has moved, and obtains information of the corresponding service. Thereafter, when the service is initiated, the corresponding terminal can receive the corresponding service.
However, for the terminal which is receiving data from the SRNC through a dedicated channel, the terminal can not simultaneously receive the MBMS Control Channel (MCCH) and the Dedicated Control Channel (DCCH) due to a lack of its capabilities. If the MCCH of the DRNC can not be read, because the terminal can not know the type of service provided from the DRNC, the terminal can not receive MBMS services even if the DRNC transmits the MBMS services to which the terminal itself has subscribed.